1. Field of the Invention
This invention relates to a disc recording and/or reproducing apparatus on which a recording track is formed for extending spirally thereon for recording/reproducing information signals. More particularly, it relates to a disc recording and/or reproducing apparatus for enabling continuous data to be recorded on or reproduced from a disc having plural recording regions having different recording densities.
2. Description of the Related Art
A variety of recording formats for optical discs as disc-shaped recording media for recording information signals have hitherto been proposed for procuring a larger recording capacity and for reliably recording information signals and for realizing highly reliable playback.
As a recording format for an optical disc, there is known a constant linear velocity (CLV) system capable of procuring a large recording capacity. With this CLV system, a disc driving motor is controlled to achieve a rotational velocity of the disc that is inversely proportional to the track radius so that the linear velocity of the recording track will be constant at any position on the disc. If the spirally extending recording track is segmented into continuous sectors each being of a predetermined length, from the inner rim towards the outer rim of the disc, data recording may be made in synchronism with predetermined clocks, while recorded data may be reproduced for data playback within a predetermined frequency range. The CLV system is advantageous in that the output power of a recording laser may be used under substantially the same recording and/or reproducing conditions for any position on the disc.
There is also known a constant angular velocity (CAV) system in which the spindle motor rotation and the recording and/or playback frequency may be kept constant. Although the CAV system is advantageous in that the motor control circuitry is simplified and the spindle motor may be reduced in size, the recording density reaches a maximum at the inner most part of the disc recording region. The number of sector marks is prescribed by the recording density. On the other hand, the radially outer part of the recording region is divided into sectors in accordance with the number of sector marks prescribed for the radially inner part of the recording region. Consequently, the recording density at the radially outer part of the recording region and becomes lower than that at the radially inner part of the recording region, as a result, the overall recording capacity of the recording region of a disc of the CAV system is lowered as compared to that of the disc of the CLV system.
As another recording format for an optical disc, there is proposed a modified CLV (M-CLV) system, which is modified to simplify the speed change control of the spindle motor adapted for rotationally driving the disc and in which advantage is taken of the larger recording capacity of the CLV system disc.
In connection with the CAV system, there is also known a modified CAV (M-CAV) system which is modified as to the defect of the small recording capacity of .the disc and in which advantage is taken of facilitated rotational control of the spindle motor. With the recording and/or reproducing apparatus, constructed in accordance with the M-CAV system, the recording frequency for the information signals is increased towards a radially outer part of the recording disc.
Meanwhile, in the case of a disc of the M-CAV or zone-CAV system having plural recording regions of different recording densities, a buffer track is provided at the boundary region between the recording regions of the different recording densities. This buffer track is provided as a transition region from a recording region of a recording density to another recording region of another recording density. Clocks or various parameters of the disc recording and/or reproducing apparatus are changed over within this transition region.
However, with the conventional disc recording and/or reproducing apparatus, sector processing is interrupted at the boundary region between the recording regions of the different recording densities of the disc during recording and/or reproduction of the information signals on or from the disc having plural recording regions with the different recording densities. Consequently, data recording or playback cannot be carried out continuously, thus leading to a lowered processing speed for recording or playback.